let input = Storefront.CustomerAccessTokenCreateInput.create(
  email: "johndoe@gmail.com",
  password: "12345"
)

let mutation = Storefront.buildMutation { $0
  .customerAccessTokenCreate(input: input) { $0
    .customerAccessToken { $0
      // [SUCCESS] Properties to get from response
      .accessToken()
      .expiresAt()
    }
    .userErrors { $0
      // [ERROR] Properties to get from response
      .field()
      .message()
    }
  }
}

let task = client.mutateGraphWith(mutation) { response, error in
  if let mutation = response?.customerAccessTokenCreate, let accessToken = mutation.customerAccessToken {
    print("[INFO] Login success: \(accessToken)")
  } else {
    print("[ERROR] Login failed: \(error)")
  }
}
task.resume()